A low-temperature, high-toughness drill pipe joint and its preparation method

Abstract

This invention discloses a low-temperature, high-toughness drill pipe joint and its preparation method, including steel grade design, smelting, billet preparation, and drill pipe joint fabrication. The joint exhibits a room temperature yield strength of 827–965 MPa, a tensile strength of 965–1103 MPa, and an elongation ≥15%; a longitudinal Charpy impact toughness ≥100 J and a transverse Charpy impact toughness ≥85 J at -20℃; and a longitudinal Charpy impact toughness ≥90 J and a transverse Charpy impact toughness ≥75 J at -40℃. This design meets the requirements for low-temperature, high-toughness drill pipe joints used in oil and gas development in extreme low-temperature environments.

Description

Technical Field

[0001] This invention relates to the field of drill pipe material technology, specifically to a low-temperature, high-toughness drill pipe joint and its preparation method. Background Technology

[0002] In cold-region oilfields, winter temperatures can drop to as low as -40°C. Winter operations place high demands on the low-temperature toughness of drill pipes to ensure safe production. Drill pipes are typically composed of a pipe body and joints connected by friction butt welding, with the drill pipe joint being a crucial component. Extreme low-temperature oil and gas extraction conditions impose even higher requirements on the strength, low-temperature toughness, and safety reliability of drill pipe joints.

[0003] Currently, ISO, API, and Chinese national standards only specify requirements for the toughness of drill pipes at -20°C. Domestic and international drill pipe manufacturers primarily produce drill pipes suitable for use in -20°C low-temperature environments. Related patents also mainly concern drill pipes of various steel grades for use in -20°C low-temperature environments. Furthermore, the relevant standards specify an excessively wide range for the yield strength of drill pipe joints, while lacking an upper limit for tensile strength. This creates difficulties in controlling the performance and quality of drill pipe joints and drill pipes themselves, and also poses safety hazards during use. Summary of the Invention

[0004] The purpose of this invention is to provide a solution that overcomes the problems of performance and quality control of drill pipe joints in the prior art at low temperatures of -40°C.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A low-temperature, high-toughness drill pipe joint, wherein the chemical composition of the joint, by mass percentage, is: C: 0.37%–0.42%, Si: 0.20%–0.35%, Mn: 1.15%–1.25%, P≤0.015%, S≤0.005%, Cr: 0.95%–1.15%, Ni: 1.05%–1.25%, Mo: 0.20%–0.30%, Nb: 0.03%–0.05%, Ti: 0.01%–0.03%, B: 0.0005%–0.0010%, Al: 0.005%–0.010%, Ca: 0.005%–0.010%, O≤0.002%, H≤0.00015%, N≤0.003%, with the balance being Fe and unavoidable impurities.

[0007] Preferably, the room temperature yield strength of the drill pipe joint is 827-965 MPa, the tensile strength is 965-1103 MPa, and the elongation is ≥15%; the longitudinal Charpy impact toughness at -20℃ is ≥100 J, and the transverse Charpy impact toughness is ≥85 J; the longitudinal Charpy impact toughness at -40℃ is ≥90 J, and the transverse Charpy impact toughness is ≥75 J.

[0008] A method for preparing a low-temperature, high-toughness drill pipe joint, based on the above-mentioned joint, includes the following steps:

[0009] S1: Steelmaking is carried out by mixing ingredients in the specified proportions to obtain molten steel;

[0010] S2: Cast molten steel into a rod-shaped continuous casting billet;

[0011] S3: Piercing and hot rolling of the continuously cast billet to obtain a thick-walled tube;

[0012] S4: Forging the thick-walled tube to obtain a drill pipe joint blank;

[0013] S5: Rough machining and heat treatment of the drill pipe joint blank to obtain a preliminary drill pipe joint;

[0014] S6: Perform finishing and threading on the initial drill pipe joint to obtain the drill pipe joint, and weld a wear-resistant strip onto the outer diameter of the final drill pipe joint.

[0015] Preferably, when casting molten steel into rod-shaped continuous casting billets, electromagnetic stirring and light reduction techniques are used to control segregation in the continuous casting billets.

[0016] Preferably, the piercing and hot rolling process involves heating the continuously cast billet in an annular heating furnace at a temperature of 1150°C to 1200°C for 90 to 120 minutes, hot piercing at 1050°C to 1150°C, hot rolling at 950°C to 1150°C, and then cooling to produce a thick-walled tube, which is then sawn.

[0017] Preferably, the die forging process involves heating the thick-walled tube to 1150℃~1200℃ and holding it at that temperature for 60~90 minutes, then rough forging at 1120℃~1170℃ and fine forging at 830℃~880℃, controlling the forging ratio to be ≥3, and air cooling after forging to obtain a drill pipe joint blank.

[0018] Preferably, the rough machining and heat treatment are as follows: the forged drill pipe joint blank is rough machined, leaving a machining allowance of 1-3 mm, and then heat-treated by using a protective atmosphere furnace heating, quenching + high temperature tempering heat treatment process to obtain the preliminary drill pipe joint.

[0019] Preferably, the heat treatment process of quenching + high-temperature tempering is as follows: the quenching heating temperature is controlled at 850℃~860℃, the holding time is 40~60 minutes, then quenching is performed, the quenching cooling medium is PAG quenching liquid, the quenching liquid temperature is controlled at 20℃~40℃ to ensure that the martensite structure is basically obtained after quenching, the tempering temperature is controlled at 600℃~620℃, the tempering time is 90~120 minutes to obtain tempered sorbite with a grain size of 8~9, and water cooling is performed after tempering.

[0020] Preferably, this includes non-destructive testing of the initial drill pipe joint after water cooling.

[0021] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a low-temperature high-toughness drill pipe joint, in which C is controlled within the range of 0.37% to 0.42% to ensure the hardenability, strength and toughness of the steel; Mn is controlled within the range of 1.15% to 1.25%; Cr is controlled within the range of 0.95% to 1.15%; Ni is controlled within the range of 1.05% to 1.25% to improve the hardenability of the steel; Mo is controlled within the range of 0.20% to 0.30% to improve the hardenability of the steel to improve strength and tempering stability; Nb is controlled within the range of 0.03% to 0.05%; Ti is controlled within the range of 0.01% to 0.03%; and B is controlled within the range of 0.01% to 0.03%. Within the range of 0.0005% to 0.0010%, the strength and toughness of the steel are improved. Al, controlled within this range, forms oxides with oxygen, acting as a deoxidizer, and forms nitrides with nitrogen, partially eliminating the adverse effects of N. Simultaneously, it refines the grain size and improves strength and toughness. Ca, controlled within the range of 0.005% to 0.010%, improves the properties and morphology of inclusions, thereby enhancing the steel's toughness. Nb, added to the steel, forms NbC and NbN with C and N, while Ti, added to the steel, forms TiC and TiN with C and N, inhibiting austenite grain growth and refining the grain size, thus improving strength and toughness. This material ratio significantly improves the performance and quality of the drill pipe joint.

[0022] Meanwhile, this invention provides a method for preparing low-temperature, high-toughness drill pipe joints. Through multiple processes, the drill pipe joints are prepared to meet the requirements for use in environments up to -40℃. Attached Figure Description

[0023] Figure 1 This is a flowchart of a method for preparing a low-temperature, high-toughness drill pipe joint according to the present invention. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0025] To overcome the deficiencies or lack of existing drill pipe joint steel design and manufacturing technology, a low-temperature high-toughness drill pipe joint with a yield strength of 827-965 MPa and a Charpy impact toughness of ≥90 J at -40℃ and its preparation method are provided.

[0026] To meet the comprehensive requirements of drill pipe joints in terms of strength, plasticity, low-temperature toughness, and weldability, their chemical composition and preparation process must be rationally designed.

[0027] In terms of composition design, this invention proposes to use C, Mn, Cr, Ni, Mo, B, V, and Ti microalloying, control harmful elements such as P, S, O, H, and N in the steel, employ Al and Si for complete deoxidation, and treat the molten steel with Ca. The roles and content ranges of each major element are as follows:

[0028] Carbon (C) is a strengthening element in steel, but too low a carbon content is detrimental to improving the hardenability and strength of the steel; too high a carbon content is detrimental to the toughness of the steel. It should be controlled within the range of 0.37% to 0.42%.

[0029] Si: A common element in steel. Its content should be controlled within the range of 0.20% to 0.35%.

[0030] Mn: Primarily used to improve the hardenability of steel, thereby increasing its strength. Its content should be controlled within the range of 1.15% to 1.25%.

[0031] Cr: Primarily used to improve the hardenability of steel, thereby increasing its strength. Its content should be controlled within the range of 0.95% to 1.15%.

[0032] Ni: Primarily used to improve the hardenability of steel, thereby increasing its strength. It should be controlled within the range of 1.05% to 1.25%.

[0033] Mo: Primarily used to improve the hardenability of steel, thereby increasing its strength and tempering stability. The concentration should be controlled within the range of 0.20% to 0.30%.

[0034] Nb: When added to steel, it forms NbC and NbN with the steel, which can inhibit the growth of austenite grains and refine the grains, thereby improving strength and toughness. The concentration should be controlled within the range of 0.03% to 0.05%.

[0035] Ti: When added to steel, it forms TiC and TiN with C and N in the steel. It has the effect of inhibiting austenite grain growth and refining grains, thereby improving strength and toughness. The content should be controlled within the range of 0.01% to 0.03%.

[0036] B: Adding it to steel can significantly improve the hardenability of the steel, thereby increasing its strength, but excessive content can cause boron embrittlement. It should be controlled within the range of 0.0005% to 0.0010%.

[0037] Al is an important deoxidizer. It forms oxides with oxygen to perform deoxidation, and forms nitrides with nitrogen to partially eliminate the adverse effects of nitrogen. It also refines grains and improves strength and toughness. Its concentration should be controlled within the range of 0.005% to 0.010%.

[0038] Ca: can improve the properties and morphology of inclusions, thereby increasing the toughness of steel. It should be controlled within the range of 0.005% to 0.010%.

[0039] P: A harmful element that mainly affects the ductility and toughness of steel. P should be controlled to ≤0.015%.

[0040] S: A harmful element that mainly affects the ductility, toughness, and corrosion resistance of steel. S should be controlled to ≤0.005%.

[0041] O: A harmful element that primarily affects the ductility, toughness, and corrosion resistance of steel. O content should be controlled to ≤0.002%.

[0042] H: A harmful element that mainly affects the ductility and toughness of steel. H should be controlled to ≤0.00015%.

[0043] Nitrogen (N): A harmful element that primarily affects the ductility and toughness of steel. Control N to ≤0.003%.

[0044] In summary, the chemical composition of the drill pipe joint, by mass percentage, is as follows: C: 0.37%–0.42%, Si: 0.20%–0.35%, Mn: 1.15%–1.25%, P≤0.015%, S≤0.005%, Cr: 0.95%–1.15%, Ni: 1.05%–1.25%, Mo: 0.20%–0.30%, Nb: 0.03%–0.05%, Ti: 0.01%–0.03%, B: 0.0005%–0.0010%, Al: 0.005%–0.010%, Ca: 0.005%–0.010%, O≤0.002%, H≤0.00015%, N≤0.003%, with the balance being Fe and unavoidable impurities.

[0045] In terms of drill pipe joint manufacturing process, the main processes are steelmaking (including ladle refining and vacuum degassing), continuous casting, hot rolling in the austenitic region, die forging, and tempering heat treatment, which enable the material to obtain a fine and uniform tempered sorbite microstructure, thereby achieving a reasonable match between the strength and toughness of the drill pipe joint.

[0046] Manufacturing process of low-temperature, high-toughness oil drill pipe joints:

[0047] ① Steelmaking: Batching, electric furnace or oxygen-blown converter steelmaking, ladle refining and vacuum degassing to obtain the above chemical composition, feeding Si-Ca wire to modify the inclusions in the steel.

[0048] ② Continuous casting: The molten steel is cast into a bar-shaped continuous casting billet. Electromagnetic stirring and light reduction technology are used in the continuous casting process to control segregation in the continuous casting billet.

[0049] ③ Piercing and hot rolling: The continuously cast billet is heated in an annular heating furnace at a temperature of 1150℃~1200℃ for 90~120 minutes. It is then hot-pierced at 1050℃~1150℃ and hot-rolled at 950℃~1150℃. After cooling, it is made into a thick-walled tube and sawn to a suitable length.

[0050] ④ Die forging: Heat the thick-walled tubular raw material to 1150℃~1200℃ and hold for 60~90 minutes. Rough forging is performed at 1120℃~1170℃, and fine forging is performed at 830℃~880℃. The forging ratio is controlled to be ≥3. After forging, the material is air-cooled.

[0051] ⑤ Rough Machining and Heat Treatment: The forged drill pipe joint blank is rough machined according to national standards, retaining a machining allowance of 1-3 mm, followed by heat treatment. A protective atmosphere furnace heating process (to prevent decarburization), quenching, and high-temperature tempering are employed. The quenching temperature is controlled at 850℃-860℃, with a holding time of 40-60 minutes, followed by quenching using PAG quenching fluid as the cooling medium. The quenching fluid temperature is controlled at 20℃-40℃ to ensure that the quenched structure is essentially entirely martensitic. The tempering temperature is controlled at 600℃-620℃, with a tempering time of 90-120 minutes to obtain fine and uniform tempered sorbite with a grain size of 8-9. Water cooling is performed after tempering to avoid potential temper brittleness. Non-destructive testing is then conducted.

[0052] ⑥ Finishing and threading: According to standards and user requirements, the drill pipe joint is finished, and API standard threads or special threads are machined. Magnetic particle testing is performed on the threads.

[0053] The present invention possesses the following performance characteristics: the low-temperature, high-toughness drill pipe joint material of the present invention, after appropriate preparation process, exhibits excellent comprehensive properties: room temperature yield strength 827–965 MPa, tensile strength 965–1103 MPa, elongation ≥15%; longitudinal Charpy impact toughness ≥100 J and transverse Charpy impact toughness ≥85 J at -20℃; longitudinal Charpy impact toughness ≥90 J and transverse Charpy impact toughness ≥75 J at -40℃. It can meet the safety requirements for use in oil drill pipe joints in extreme low-temperature environments.

[0054] Example 1

[0055] The chemical composition of the low-temperature, high-toughness oil drill pipe joint material provided in this embodiment of the invention is as follows: C: 0.42%, Si: 0.35%, Mn: 1.25%, P: 0.010%, S: 0.003%, Cr: 1.15%, Mo: 0.3%, Ni: 1.25%, Nb: 0.039%, Ti: 0.021%, B: 0.001%, Ca: 0.005%, Al: 0.007%, O: 0.002%, H: 0.00015%, N: 0.003%, with the balance being Fe and unavoidable impurities.

[0056] This invention also provides a method for preparing a low-temperature, high-toughness drill pipe joint, comprising the following steps:

[0057] ① Steelmaking: Batching, electric furnace steelmaking, ladle refining and vacuum degassing to obtain the above chemical composition, which is Si-Ca wire to modify inclusions in steel.

[0058] ② Continuous casting: The molten steel is cast into a bar-shaped continuous casting billet. Electromagnetic stirring and light reduction technology are used in the continuous casting process to control segregation in the continuous casting billet.

[0059] ③ Piercing and hot rolling: The continuously cast billet is heated in an annular heating furnace at a temperature of 1150℃ for 120 minutes. It is then hot-pierced at 1150℃, hot-rolled at 1150℃, and then cooled to form a thick-walled tube, which is then sawn to a suitable length.

[0060] ④ Die forging: Heat the thick-walled tubular raw material to 1200℃ and hold for 90 minutes. Rough forging is performed at 1170℃ and finish forging at 880℃. The forging ratio is controlled at 3. After forging, air cool.

[0061] ⑤ Rough Machining and Heat Treatment: The forged drill pipe joint blank is rough machined, leaving a machining allowance of 1mm, and then heat-treated. A protective atmosphere furnace heating process (to prevent decarburization), followed by quenching and high-temperature tempering is used. The quenching temperature is 860℃, and the holding time is 60 minutes, followed by quenching using PAG quenching fluid as the cooling medium. The quenching fluid temperature is controlled at 40℃, and the time from the quenching heating temperature to the quenching medium is 5 seconds to ensure that the quenched structure is essentially complete with martensite. The tempering temperature is 620℃, and the tempering time is 90 minutes to obtain fine and uniform tempered sorbite with a grain size of grade 9. After tempering, water cooling is performed to avoid potential temper brittleness. Non-destructive testing is then conducted.

[0062] ⑥ Finishing and threading: According to standards and user requirements, the drill pipe joint is finished, and API standard threads or special threads are machined. Magnetic particle testing is performed on the threads.

[0063] The performance of the oil drill pipe joint prepared according to the above composition and process is as follows: room temperature yield strength 943 MPa, tensile strength greater than 1069 MPa, elongation 25%; longitudinal Charpy impact toughness 136 J and transverse Charpy impact toughness 116 J at -20℃; longitudinal Charpy impact toughness 125 J and transverse Charpy impact toughness 106 J at -40℃. It possesses high strength and high / low temperature toughness, meeting the safety requirements for oil drill pipe joints in low-temperature environments down to -40℃.

[0064] Example 2

[0065] The chemical composition of the low-temperature, high-toughness oil drill pipe joint material provided in Example 2 of this invention is as follows: C: 0.41%, Si: 0.20%, Mn: 1.15%, P: 0.011%, S: 0.002%, Cr: 0.97%, Mo: 0.2%, Ni: 1.05%, Nb: 0.030%, Ti: 0.030%, B: 0.005%, Ca: 0.007%, Al: 0.008%, O: 0.001%, H: 0.00015%, N: 0.003%, with the balance being Fe and unavoidable impurities.

[0066] Embodiment 2 of the present invention also provides a method for preparing a low-temperature high-toughness drill pipe joint, comprising the following steps:

[0067] ① Steelmaking: Batching, oxygen-blown converter steelmaking, ladle refining and vacuum degassing to obtain the above chemical composition, which is Si-Ca wire to modify the inclusions in the steel.

[0068] ② Continuous casting: The molten steel is cast into a bar-shaped continuous casting billet. Electromagnetic stirring and light reduction technology are used in the continuous casting process to control segregation in the continuous casting billet.

[0069] ③ Piercing and hot rolling: The continuously cast billet is heated in an annular heating furnace at a temperature of 1200℃ for 100 minutes. It is then hot-pierced at 1100℃ and hot-rolled at 1050℃. After cooling, it is made into a thick-walled tube and sawn to a suitable length.

[0070] ④ Die forging: Heat the thick-walled tubular raw material to 1175℃ and hold for 70 minutes. Rough forging is performed at 1140℃ and finish forging at 850℃. The forging ratio is controlled at 4. After forging, air cool.

[0071] ⑤ Rough Machining and Heat Treatment: The forged drill pipe joint blank is rough machined, leaving a machining allowance of 2mm, and then heat-treated. A protective atmosphere furnace heating, quenching, and high-temperature tempering heat treatment process is adopted. The quenching heating temperature is 854℃, the holding time is 50 minutes, followed by quenching using PAG quenching fluid as the cooling medium. The quenching fluid temperature is controlled at 30℃, and the time from the quenching heating temperature to the quenching medium is 3 seconds to ensure that the quenched structure is basically complete with martensite. The tempering temperature is 610℃, and the tempering time is 110 minutes to obtain fine and uniform tempered sorbite with a grain size of grade 8. After tempering, water cooling is performed to avoid potential temper brittleness. Non-destructive testing is then performed.

[0072] ⑥ Finishing and threading: According to standards and user requirements, the drill pipe joint is finished, and API standard threads or special threads are machined. Magnetic particle testing is performed on the threads.

[0073] The performance of the oil drill pipe joint prepared according to the above composition and process is as follows: room temperature yield strength 923 MPa, tensile strength greater than 1048 MPa, elongation 24%; longitudinal Charpy impact toughness 129 J and transverse Charpy impact toughness 110 J at -20℃; longitudinal Charpy impact toughness 118 J and transverse Charpy impact toughness 100 J at -40℃. It possesses high strength and high / low temperature toughness, meeting the safety requirements for oil drill pipe joints in low-temperature environments down to -40℃.

[0074] Example 3

[0075] The chemical composition of the low-temperature, high-toughness oil drill pipe joint material provided in Example 3 of this invention is as follows: C: 0.38%, Si: 0.29%, Mn: 1.19%, P: 0.013%, S: 0.002%, Cr: 1.10%, Mo: 0.24%, Ni: 1.11%, Nb: 0.034%, Ti: 0.016%, B: 0.006%, Ca: 0.006%, Al: 0.005%, O: 0.002%, H: 0.0001%, N: 0.002%, with the balance being Fe and unavoidable impurities.

[0076] Embodiment 3 of the present invention also provides a method for preparing a low-temperature high-toughness drill pipe joint, comprising the following steps:

[0077] ① Steelmaking: Batching, electric furnace steelmaking, ladle refining and vacuum degassing to obtain the above chemical composition, which is Si-Ca wire to modify inclusions in steel.

[0078] ② Continuous casting: The molten steel is cast into a bar-shaped continuous casting billet. Electromagnetic stirring and light reduction technology are used in the continuous casting process to control segregation in the continuous casting billet.

[0079] ③ Piercing and hot rolling: The continuously cast billet is heated in an annular heating furnace at a temperature of 1200℃ for 90 minutes. It is then hot-pierced at 1050℃, hot-rolled at 950℃, and then cooled to form a thick-walled tube, which is then sawn to the appropriate length.

[0080] ④ Die forging: Heat the thick-walled tubular raw material to 1150℃ and hold for 60 minutes. Rough forging is performed at 1120℃ and finish forging at 830℃. The forging ratio is controlled at 4. After forging, air cool.

[0081] ⑤ Rough Machining and Heat Treatment: The forged drill pipe joint blank is rough machined, leaving a machining allowance of 3mm, and then heat-treated. A protective atmosphere furnace heating, quenching, and high-temperature tempering heat treatment process is adopted. The quenching heating temperature is 850℃, the holding time is 50 minutes, followed by quenching using PAG quenching fluid as the cooling medium. The quenching fluid temperature is controlled at 40℃, and the time from the quenching heating temperature to the quenching medium is 4 seconds to ensure that the quenched structure is basically complete with martensite. The tempering temperature is 600℃, and the tempering time is 90 minutes to obtain fine and uniform tempered sorbite with a grain size of grade 9. After tempering, water cooling is performed to avoid potential temper brittleness. Non-destructive testing is then performed.

[0082] ⑥ Finishing and threading: According to standards and user requirements, the drill pipe joint is finished, and API standard threads or special threads are machined. Magnetic particle testing is performed on the threads.

[0083] The performance of the oil drill pipe joint prepared according to the above composition and process is as follows: room temperature yield strength 928 MPa, tensile strength greater than 1054 MPa, elongation 24%; longitudinal Charpy impact toughness 127 J and transverse Charpy impact toughness 108 J at -20℃; longitudinal Charpy impact toughness 117 J and transverse Charpy impact toughness 99 J at -40℃. It possesses high strength and high / low temperature toughness, meeting the safety requirements for oil drill pipe joints in low-temperature environments down to -40℃.

[0084] Example 4

[0085] The chemical composition of the low-temperature, high-toughness oil drill pipe joint material provided in Example 3 of this invention is as follows: C: 0.37%, Si: 0.24%, Mn: 1.23%, P: 0.011%, S: 0.003%, Cr: 1.01%, Mo: 0.28%, Ni: 1.16%, Nb: 0.05%, Ti: 0.010%, B: 0.009%, Ca: 0.010%, Al: 0.009%, O: 0.003%, H: 0.0001%, N: 0.002%, with the balance being Fe and unavoidable impurities.

[0086] Embodiment 4 of the present invention also provides a method for preparing a low-temperature high-toughness drill pipe joint, comprising the following steps:

[0087] ① Steelmaking: Batching, oxygen-blown converter steelmaking, ladle refining and vacuum degassing to obtain the above chemical composition, which is Si-Ca wire to modify the inclusions in the steel.

[0088] ② Continuous casting: The molten steel is cast into a bar-shaped continuous casting billet. Electromagnetic stirring and light reduction technology are used in the continuous casting process to control segregation in the continuous casting billet.

[0089] ③ Piercing and hot rolling: The continuously cast billet is heated in an annular heating furnace at a temperature of 1150℃ for 120 minutes. It is then hot-pierced at 1150℃, hot-rolled at 1150℃, and then cooled to form a thick-walled tube, which is then sawn to a suitable length.

[0090] ④ Die forging: Heat the thick-walled tubular raw material to 1200℃ and hold for 90 minutes. Rough forging is performed at 1170℃ and finish forging at 880℃. The forging ratio is controlled at 3. After forging, air cool.

[0091] ⑤ Rough Machining and Heat Treatment: The forged drill pipe joint blank is rough machined, leaving a machining allowance of 3mm, and then heat treated. A protective atmosphere furnace heating, quenching, and high-temperature tempering heat treatment process is adopted. The quenching heating temperature is 860℃, the holding time is 60 minutes, followed by quenching using PAG quenching fluid as the cooling medium. The quenching fluid temperature is controlled at 40℃, and the time from the quenching heating temperature to the quenching medium is 5 seconds to ensure that the quenched structure is basically complete with martensite. The tempering temperature is 620℃, and the tempering time is 120 minutes to obtain fine and uniform tempered sorbite with a grain size of grade 8. After tempering, water cooling is performed to avoid potential temper brittleness. Non-destructive testing is then performed.

[0092] ⑥ Finishing and threading: According to standards and user requirements, the drill pipe joint is finished, and API standard threads or special threads are machined. Magnetic particle testing is performed on the threads.

[0093] The performance of the oil drill pipe joint prepared according to the above composition and process is as follows: room temperature yield strength 916 MPa, tensile strength greater than 1042 MPa, elongation 25%; longitudinal Charpy impact toughness 132 J and transverse Charpy impact toughness 112 J at -20℃; longitudinal Charpy impact toughness 123 J and transverse Charpy impact toughness 105 J at -40℃. It possesses high strength and high / low temperature toughness, meeting the safety requirements for oil drill pipe joints in low-temperature environments down to -40℃.

[0094] Example 5

[0095] The chemical composition of the low-temperature, high-toughness oil drill pipe joint material provided in Example 5 of this invention is as follows: C: 0.40%, Si: 0.27%, Mn: 1.21%, P: 0.010%, S: 0.005%, Cr: 1.04%, Mo: 0.25%, Ni: 1.19%, Nb: 0.046%, Ti: 0.024%, B: 0.0008%, Ca: 0.008%, Al: 0.010%, O: 0.002%, H: 0.0001%, N: 0.002%, with the balance being Fe and unavoidable impurities.

[0096] Embodiment 5 of the present invention also provides a method for preparing a low-temperature high-toughness drill pipe joint, comprising the following steps:

[0097] ① Steelmaking: Batching, electric furnace steelmaking, ladle refining and vacuum degassing to obtain the above chemical composition, which is Si-Ca wire to modify inclusions in steel.

[0098] ② Continuous casting: The molten steel is cast into a bar-shaped continuous casting billet. Electromagnetic stirring and light reduction technology are used in the continuous casting process to control segregation in the continuous casting billet.

[0099] ③ Piercing and hot rolling: The continuously cast billet is heated in an annular heating furnace at a temperature of 1150℃ for 120 minutes. It is then hot-pierced at 1150℃, hot-rolled at 1150℃, and then cooled to form a thick-walled tube, which is then sawn to a suitable length.

[0100] ④ Die forging: Heat the thick-walled tubular raw material to 1200℃ and hold for 90 minutes. Rough forging is performed at 1170℃ and finish forging at 880℃. The forging ratio is controlled at 3. After forging, air cool.

[0101] ⑤ Rough Machining and Heat Treatment: The forged drill pipe joint blank is rough machined, leaving a machining allowance of 3mm, and then heat-treated. A protective atmosphere furnace heating, quenching, and high-temperature tempering heat treatment process is adopted. The quenching heating temperature is 860℃, the holding time is 40 minutes, followed by quenching using PAG quenching fluid as the cooling medium. The quenching fluid temperature is controlled at 40℃, and the time from the quenching heating temperature to the quenching medium is 5 seconds to ensure that the quenched structure is basically complete with martensite. The tempering temperature is 620℃, and the tempering time is 120 minutes to obtain fine and uniform tempered sorbite with a grain size of grade 8. After tempering, water cooling is performed to avoid potential temper brittleness. Non-destructive testing is then performed.

[0102] ⑥ Finishing and threading: According to standards and user requirements, the drill pipe joint is finished, and API standard threads or special threads are machined. Magnetic particle testing is performed on the threads.

[0103] The performance of the oil drill pipe joint prepared according to the above composition and process is as follows: room temperature yield strength 908 MPa, tensile strength greater than 1033 MPa, elongation 25%; longitudinal Charpy impact toughness 136 J and transverse Charpy impact toughness 116 J at -20℃; longitudinal Charpy impact toughness 125 J and transverse Charpy impact toughness 106 J at -40℃. It possesses high strength and high / low temperature toughness, meeting the safety requirements for oil drill pipe joints in low-temperature environments down to -40℃.

[0104] Example 6

[0105] The chemical composition of the low-temperature, high-toughness oil drill pipe joint material provided in Example 6 of this invention is as follows: C: 0.39%, Si: 0.33%, Mn: 1.20%, P: 0.015%, S: 0.002%, Cr: 0.95%, Mo: 0.26%, Ni: 1.14%, Nb: 0.040%, Ti: 0.020%, B: 0.0007%, Ca: 0.009%, Al: 0.006%, O: 0.002%, H: 0.0001%, N: 0.002%, with the balance being Fe and unavoidable impurities.

[0106] Embodiment 6 of the present invention also provides a method for preparing a low-temperature high-toughness drill pipe joint, comprising the following steps:

[0107] ① Steelmaking: Batching, oxygen-blown converter steelmaking, ladle refining and vacuum degassing to obtain the above chemical composition, which is Si-Ca wire to modify the inclusions in the steel.

[0108] ② Continuous casting: The molten steel is cast into a bar-shaped continuous casting billet. Electromagnetic stirring and light reduction technology are used in the continuous casting process to control segregation in the continuous casting billet.

[0109] ③ Piercing and hot rolling: The continuously cast billet is heated in an annular heating furnace at a temperature of 1150℃ for 120 minutes. It is then hot-pierced at 1150℃, hot-rolled at 1150℃, and then cooled to form a thick-walled tube, which is then sawn to a suitable length.

[0110] ④ Die forging: Heat the thick-walled tubular raw material to 1200℃ and hold for 90 minutes. Rough forging is performed at 1170℃ and finish forging at 880℃. The forging ratio is controlled at 3. After forging, air cool.

[0111] ⑤ Rough Machining and Heat Treatment: The forged drill pipe joint blank is rough machined, leaving a machining allowance of 3mm, and then heat-treated. A protective atmosphere furnace heating, quenching, and high-temperature tempering heat treatment process is adopted. The quenching heating temperature is 860℃, the holding time is 60 minutes, followed by quenching using PAG quenching fluid as the cooling medium. The quenching fluid temperature is controlled at 40℃, and the time from the quenching heating temperature to the quenching medium is 5 seconds to ensure that the quenched structure is basically complete with martensite. The tempering temperature is 620℃, and the tempering time is 90 minutes to obtain fine and uniform tempered sorbite with a grain size of grade 9. After tempering, water cooling is performed to avoid potential temper brittleness. Non-destructive testing is then performed.

[0112] ⑥ Finishing and threading: According to standards and user requirements, the drill pipe joint is finished, and API standard threads or special threads are machined. Magnetic particle testing is performed on the threads.

[0113] The performance of the oil drill pipe joint prepared according to the above composition and process is as follows: room temperature yield strength 943 MPa, tensile strength greater than 1069 MPa, elongation 23%; longitudinal Charpy impact toughness 119 J and transverse Charpy impact toughness 101 J at -20℃; longitudinal Charpy impact toughness 109 J and transverse Charpy impact toughness 93 J at -40℃. It possesses high strength and high / low temperature toughness, meeting the safety requirements for oil drill pipe joints in a -40℃ low-temperature environment.

[0114] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art, guided by the specification, can make many other modifications without departing from the scope of the claims of the present invention, and all of these modifications are within the scope of protection of the present invention.

Claims

1. A cryogenic high toughness drill pipe joint, characterized by, The chemical composition of the joint in percentage by mass is: C: 0.37%~0.42%, Si: 0.20%~0.35%, Mn: 1.15%~1.25%, P≤0.015%, S≤0.005%, Cr: 0.95%~1.15%, Ni: 1.05%~1.25%, Mo: 0.20%~0.30%, Nb: 0.03%~0.05%, Ti: 0.01%~0.03%, B: 0.0005%~0.0010%, Al: 0.005%~0.010%, Ca: 0.005%~0.010%, O≤0.002%, H≤0.00015%, N≤0.003%, the balance being Fe and inevitable impurities; The drill pipe joint has a room temperature yield strength of 827~965 MPa, a tensile strength of 965~1103 MPa, and an elongation of ≥15%; the longitudinal Charpy impact toughness at-20 ℃ is ≥100 J, and the transverse Charpy impact toughness is ≥85 J; the longitudinal Charpy impact toughness at-40 ℃ is ≥90 J, and the transverse Charpy impact toughness is ≥75 J.

2. A method of producing a cryogenic high toughness drill pipe joint based on the cryogenic high toughness drill pipe joint of claim 1, characterized in that, The method comprises the following steps: S1: proportioning and smelting to obtain a molten steel; S2: casting the molten steel into a rod-shaped continuous casting billet; S3: performing piercing and hot continuous rolling on the continuous casting billet to obtain a thick-walled pipe; S4: performing die forging treatment on the thick-walled pipe to obtain a drill pipe joint blank; S5: performing rough machining and heat treatment on the drill pipe joint blank to obtain a preliminary drill pipe joint; S6: performing finishing and threading processing on the preliminary drill pipe joint to obtain a drill pipe joint, and welding a wear-resistant strip on the outer diameter of the final drill pipe joint.

3. The method of claim 2, wherein the cryogenic high toughness drill pipe joint is prepared by the steps of: When the molten steel is cast into a rod-shaped continuous casting billet, electromagnetic stirring and light pressing down technology are used to control segregation in the continuous casting rod billet.

4. The method of claim 2, wherein the cryogenic high toughness drill pipe joint is prepared by the steps of: The piercing and hot continuous rolling are specifically as follows: the continuous casting billet is heated in a ring-shaped heating furnace, the heating furnace temperature is 1150 ℃~1200 ℃, the heating time is 90~120 minutes, the continuous casting billet is hot pierced at 1050 ℃~1150 ℃, and hot continuous rolling is performed at 950 ℃~1150 ℃, and then the thick-walled pipe is obtained after cooling and sawing.

5. The method of claim 2, wherein the cryogenic high toughness drill pipe joint is prepared by the steps of: The die forging is specifically as follows: the thick-walled pipe is heated to 1150 ℃~1200 ℃ and kept for 60~90 minutes, rough forging is performed at 1120 ℃~1170 ℃, and finishing forging is performed at 830 ℃~880 ℃, the forging ratio is controlled to be ≥3, and the drill pipe joint blank is obtained after air cooling.

6. The method of claim 2, wherein the cryogenic high toughness drill pipe joint is prepared by the steps of: The rough machining and heat treatment are specifically as follows: the drill pipe joint blank after forging is roughly machined, a machining allowance of 1~3 mm is reserved, and then heat treatment is performed, a heat treatment process of protective atmosphere furnace heating, quenching + high-temperature tempering is adopted, and a preliminary drill pipe joint is obtained.

7. The method of claim 6, wherein the cryogenic high toughness drill pipe joint is prepared by the steps of: The heat treatment process of quenching + high-temperature tempering is specifically as follows: the quenching heating temperature is controlled to be 850 ℃~860 ℃, the holding time is 40~60 minutes, then quenching is performed, the quenching cooling medium is PAG quenching liquid, the quenching liquid temperature is controlled to be 20 ℃~40 ℃, the entire martensite structure is ensured after quenching, the tempering temperature is controlled to be 600 ℃~620 ℃, the tempering time is 90~120 minutes, tempered sorbite is obtained, the grain size is 8~9 levels, and water cooling is performed after tempering.

8. The method of claim 7, wherein the cryogenic high toughness drill pipe joint is prepared by the steps of: Including non-destructive testing of the water-cooled primary drill pipe joint.

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